Communication system



Aug. 26j, '1947.

l. A. KRAUSE COMMUNCATION SYSTEM Filed April 20, 1944 4 Sheets-Sheet l NW @kolab QQ MX SS lug. 2 6, 1947.

l. A. KRAUSE COMMUNICATION SYSTEM Filed April 2o, 1944 4 Sheets-Sheet 2 www E X To V2 Tol/1 MHS/UNG WV wan/,4.4 Mapu ,4 rfa fm/D MAS/(0 PaLsf OUTPUT mmm ATTORNEY Aug. Z6, 1947.

l. A. KRAUSE COMMUNICATION SYSTEM Filed April 20,- 1944 4 Sheets-Sheet I5 Tv, QQ l c INVENTOR. /m//A/G 4. KfW/055 -BY /y AQ?? Armin/E7 fwn,

Aug! 26, w47. 1. A. KRAUSE 2,426,225

COMMUNICATION SYSTEM Filed April 20. 1944 4 Sheets-Shet 4 I N VEN TOR. #Pw/VG f1. mwN/5E Ziff/2%?? ATTWIVEY Patented ug. 26, 1947 UNITED STATES 2,426,225 COMMUNICATIQN 'SYSTEM Irving A. Krause, Jersey City, AFederal Telephone and N. J., assigner to Radio` Corporation,

New York, N, Y., a corporationof` Delaware Application April Z0, 1944, Serial No. 531,859

20 Claims.

The present invention relatesto communication systems yand more particularly to a communication system having means for preventing or ren,- dering more diicult unauthorized reception of the transmitted intelligence.

One object of the invention is to provide a method and means ifor modulating a pulse subcarrier so that the modulating intelligence will be undetectable by the.usual receiving aparatus; and

Another object-of the invention isy to provide a method and means-for receiving and detecting such modulated pulses, and for minimizing interference.

One of the -features of `the invention is to provide means for generating a train of pulses constituting a sub-.carrier vwave, modulating, either by amplitude, time or other pulse characteristic, the odd pulsesof the train out of ,phase with the even pulses by a signal-wave representing the intelligence which it is desiredto transmit, and recombining the modulated pulses in theorder of their generation. At a, receiving point, the modulated pulses'are separated according to odd and even pulses, whereupon at least one of the groups of'separated pulses is detected.

An additional feature of the invention comprises providing means ior reoeivingthe vmodulated pulses at a point remote from the transmission thereofseparating the odd group of pulses from the even group,.demodulating,and/ or filtering to obtain theV audio Wave defined thereby, shifting the phase of one of the Waves by an amount sufficient for recombiningv with the other wave, and reproducing the intelligence thereof.

A further-feature of the invention is to provide, in addition to the dilierent phase modulationof the odd and even pulses, a further modulating energylin the form of. a .masking Wave,;this additional energy being applied in a vmanner to the odd and evenpulses. so that by inversion and mixing or-direct mixingl of the tvlol audio waves produced from the odd vand even pulses, as the case may be, the masking wave is removed fromi the desired intelligence Wave.

Other objects and Afeatures of .the invention will be apparent from the following-description of a preferred form .of thev inventionk and from the drawings', inwhich:

Fig. 1V is a circuit diagram of a preierrediorm of transmitter lembodying the .present invention;

Fig. 2 is a set of curves usedjn explaining the operation of the circuit of Fig. l;

. Fig. 3 is a circuit diagram voi a preferred -orm of receiver embodying the, present invention;

(Cl. Z50-,6)

y2 Fig. ,41s acircuit diagram of a modiiied-iormof transmittenelnbodying the present invention;

Fig. 5 isanalternl tive form of demodulator for use in thecircuit of Fig. 3; and 5 Fig. 6 is a graphical villustration used in explaining 'the operation of the demodulator -oi Fig. 5.

For the,` 1purpose of illustrating Vmy, invention, I have shown -in'Figs l -to 3 the principles thereof bvmeans Yof lamplitude modulation. In Fig.l 1 isv shown argenerator 4 having a substantially sine Wave output .such as indicated by the waveform 6. This wave liA is :of sub-carrier frequency, that is, vlovverfthan the Y'frequency 'oi the usual R.. F. or ultra high frequency carrier wave but higher than that of an audio signal.

A' know Wave Shaper 8 translates the sine Wavev (i .into asubstantially square wave I0. A known Wavev inverter :l2 inverts by 130 the square'wavezl asv indicated by square wave lll. Theshaper 8 and' invertor l2, of course, may be replaced byV ar A,multivibrationv circuit wherein square Waves vof opposite lpolarity 4may be obtained.

The outputs Yoi wavezshaper 8 and inverter I2 areffedto-two differentiators `Hi and I8, respectively,foi theLcharacter adaptedto translate each square vpulse portion of the'vvaves in and I4. into two sets :of Anarrowvzidth positivel and negative pulses` as indicated .at .20 and,y 2,2, respectively. The pulses 2l) and 2,2 are applied to two tetrodes where the negative p lses areelirninated and the postive` pulses are amplitude .modulated This isaccomplished by biasing .each 'of the two tetrodes N71-,and V2 to cut-(oli. Vrconducts only the positive `pulses ofwave and V2 conducts only thepositive pulses of Wave`2k2. `Since the positive `pulses oigvvave 20 alternate with the positive lnulsesgoi, wave122, the pulses conducted by `V1V will be termed the odd pulses, and the pulses conducted by lV2 the even pulses.

kThe screenzgrdSfZQ and. .25 of tubes V1 and V2 are respectively connected Vvto opposite ends of the seccndarvcoil vof a transformer ,28. The primary ;of transformer'vlS is connected to a source of audio. .signals representing the intelligence which it `is -desiled to transmit. It Willbe seen that: ydue to the opposite polarity existing at the ends of the transformer secondary, screen grids 214,?11d2 vlglbe energized 180 out of phase Foy the audioinpllt. ,.Srince V1 :Conducts only odd pulses and'V V2 conditi-dtsy only even pulses, the oddzpulseszairldthe evenpulses will be audio modulated` out :of yphase tofwone another. The 32, respectively representing waveforms 30 and agradece the outputs of V1 and V2, will thus have different amplitudes depending on the characteristics of the modulating signal applied to transformer 28.

The outputs of tubes V1 and V2 are combined at `34 across resistor R, the combined pulse energy being represented by waveform 3S. This Wave te is then fed to an R.F. translate;1 38 where the audio pulses are amplified and transformed into R.F. pulses at a given carrier frequency for transmission from antenna 40.

In addition to the mixing of the two groups of pulses modulated 180 out-of-phase, the pulses may be further modulated by a given masking signal, the further modulation being added to the pulse output from tubes V1 and vV2 in proper phase relation according to the time spacing of successive pulses. This further modulation may take the form of a saw-tooth wave 42 from source 43 applied to the mid-point of the secondary winding of transformer y28 Iby connection 44. The saw-tooth voltage Wave 42 thereby energizes both screen grids 24 and 2t in phase, as contrasted to the out-of-phase energization of these grids by the audio signal input taken across the ends of the transformer secondary Winding, Y

To summarize the operation of the transmitter circuit of Fig. 1, reference is now made to the curves of Fig. 2. Curves a and b illustrate the pulse outputs 36 and 32 of tubes V1 and V2, respectively, in the absence of any modulation. An audio modulating signal is shown in curve c, the solid -line 45 representing the voltage at one end of the secondary Winding of transformer 28, and the broken line 4l representing the voltage at the other end of the Winding.

The el'ects of the modulating Wave c 0n the pulses of curves a and b are shown in curves d and e, respectively. The resulting Wave 35 appearing at point 34 is represented byl Curve The in-phase masking Wave 42 is shown in g, and its effect on the output wave f is shown in h, both odd and even pulses being modulated in phase in the order ofY their generationV as eX- plained above. While the pulses of the curves of Fig. 2 have all been drawn as being of positive polarity, it will be understood that their actual polarity according to the-circuit of Fig. 1 will be as indicated at the diierent points in the circuit. The masking Wave 42 maybe regarded as having the same eiect on the transmitted pulses as a` non-pulse interference signal such, for example, as an amplitude modulated carrier.

A form of receiver according to the present invention is shown in Fig. 3. IThe energy transmitted from antenna 45 of Fig. l, after being received on antenna 46, is passed through detector 48. The detector 48 demodulates the R.F. carrier energy supplied by translator 38 into a series of sub-carrier pulses substantially` identical to the pulse train 3S of Figs. 1 and 2. Receiving the pulse output of detector 48 are a rst keyer 5G, a second keyer 52 andra timer circuit 54. Keyer D handles only the odd pulses of thev train while keyer 52 handles only the even pulses. Keyer 50, keyer 52 and timer 54 each' include an electron discharge tube biased to cut-oir" as illustrated.

By providing the timer 54 with a plate circuit 56 tuned to the recurrence frequency of the pulse train 36 (curves f and h, Fig. 2), the `received pulses Will `be passed through a circuit 58 to the grid of a triode 65 constituting one element of ay multivibrator k62. Multivibrator 62'is provided with a second triode $4, 'the grids and plates of thetwo'tubes beingcross-'connected in normal manner. Y

Multivibrator 62 is adjusted to operate at onehalf the pulse rate, the pulses received on the grid of triode 6!) over circuit 58 serving to key the operation of the multivibrator at one-half the two plate circuits of the multivibrator 62 are ccnnected to screen grids y66 and 68 in the electron discharge devices of the rst keyer circuit 55 and the second keyer circuit 52, respectively. The screen grid 66 in the rst keyer tube l, is alternately driven positive and negative at the rate of operation of the multivibrator. The same cycle of operation applies to the screen grid S8 of the secondkeyer tubeV 12, except that when grid is driven positively the grid 68 is driven negatively and vice versa. v f

Consider now the pulses received by the control'grid I4 of the iirst keyer tube '19. Odd pulses appearing on the grid 14 in coincidence with the positive potential conditions of grid 56 act to .ake the tube 'lil conductive. When the following even pulse appears on the grid lll, the screen grid 65 having been driven negative by the acu tion of multivibrator A(i2, the tube remains at cutc thereby blocking the even pulse.

The reverse action occurs in the second keyer circuit `52. Since one plate circuit of multivibrator 52 is positive when theother plate circuit is negative, the polarity of screen grid 68 will always be opposite in polarity to the polarity of screen grid 6B. Tube 1'2 Will therefore conduct the even pulsesV and block the odd pulses. Y A pair of resistance-condenser combinations 22 and 84 form parts of the plate circuits of keyers 59 combinations 82 and B4 are chosen of such values that the time constants of the combinations operate to `filter out the pulses, thereby reproducing with ra minimum of distortion the audio envelope Wave representing the intelligence applied to the-primary of transformer 28 of Fig. 1.

Since the audio wave of the odd pulses passed by keyer 50 is 180 out of phase with the audio Wave of the even pulses passed by Ikeyer 52, the audio Waves reproduced bythe tvvo keyer cir cuits at their output connections 15 and Il are Y 180out of phase.v By applying the output wave of one of the keyers, such as 52, to a phase invertor 'I6 for 180 inversion and then combining the inverted wave output by connection 'i9 to the wave of output'connection 15, a more accurate reproduction of the intelligence VWave is eiected than that represented by the separate outputs of keyer circuits 59 and 52. The combined audio wave is then amplified at i8 and applied to speaker 8U. Y

.It should be noted that either of the audio YWaves appearing in the plate circuits of keyers 5i) and 52 defines the transmitted intelligence. rThe purpose of mixing the two audio Waves is to reproduce the intelligence to a, higher degree of accuracy than is possible through theV utilization of either wave alone. The output of one of the keyer circuits may, of course, be applied directly to amplifier '18 and subsequently reproduced'. This would dispense with the necessity Vof employing a second keyer circuit, although as previously and 52,V respectively. The elements of these mentioned, accuracy .of definition would be sacn riced to a certain degree.

A In caseswherethe -masking signal'l2 is utilized, or an interference signaLsuch as van A. M. modulated carrier, both keyer circuits 5|! and 52 must be employed. The reasonfor this is that the masking signal and/or interference signal present on the same carrier, asithe .case may be, is. appliedxin phase to both odd and even pulses. If nowthe even pulseenvelope wave .is phase inverted inthe receiver by inverting circuit 1B, the mixing of vthe two envelopesin amplifier i8 will cancel outthe masking signal and. any such interferencelsignal leaving only tthe audio modulation representing the desired intelligence.

-IIt will be obvious thatthe masking signal d'2 may itself represent' intelligence. In suchv an event the odd and even envelope waves may be mixed directly by moving switch contact 85 from contact 85 to contact Si thereby ley-passing phase invertor T6. This would cancel the signals applied to the pulses through the primary of transformer 23, Fig. l., leaving the signal applied to the center tap of the secondary of the transformer 28. r Thus, either of the vmodulating input signals `of Fig. l may carrythe actual message, or, if' desired, they may represent separate messages. Where the signal @l2 is the desired intelligence, then interference minimizing must be carried out by a' suitable blo cking'arrangement.

AIn Figs. 1l, 5 and 6 I have shown the principles of my invention by Way of time modulation. Fig. 4 illustrates a P. T. M. (pulse'time modulation) transmitter including a generator it@ for producing a base wave |52, 'The output of generator Idil is fed both to a 90 phase shifter Hifi and to one primary winding |55 of a transformer lii. The output of phase shifter Hill is fed yto one primary winding |01 of a second transformer l which is similar to transformer |96.

Transformer we constitutes part of a T. M. modulator H6. Also included in the modulator H5 is a pair of electron discharge tubes H2 and H4 connected together in push-pull fashion, the grids of tubes H2 and H4 being fed from opposite ends of the split .secondary winding |59, iii of transformer |06. The anode circuits of tubes H2 and lill are joined together at Il@ and the combined outputs of the tubes fed to a pulse clipper and Shaper H. Transformer |58 .constitutes part of a second T. M. modulator 25 which is similar to modulator HB.

'Also shown in Fig. 4. is a transformer Esa which may be identical to the transformer 25 in Fig. 1. The ends of the secondary winding -of transformer 28a are connected respectively to a second primary winding |22 of transformer .|95 and to a second primary winding |24 of transformer |88. The audio-signal representing the intelligence which it is desired to transmit is applied to the primaryv winding Vof transformer 28a in the same manner that'the audio-signal is applied to the primary winding of transformer 28 of Fig. l. A masking signal 2 which may be identical to the masking signal of Fig. l is applied to-the center-tapped vsecondary of transformer 28asimilarly as shown in Fig. 1. The combined TM outputs of modulators HB and |29 are fed to anR. F. translator i351 and then transmitted from an antenna |32.

Referring particularly to the modulatorcircuit HD, it will be understood that it amplies and, in effect, full-wave rectifies the wave |52, to obtain a cusper wave H3. `Time modulation of the. `lcusperA wave is Aproduced by applying thev i pulses |38 time modulated according to to primary. coil: :|22 .ofithe transformer |06. The signal intelligence operates,.k in effect, to vary Athe wave .L02 relative. to its zero axis as regards the full-wave-rectication. This relative variation between the 'wave and the zero axis'thereof is illustrated by theupper and lower;modulationilimits vlllZa and ,|9211 ".When the inputsignal varies the vrelative relation between the zero axis and the wave :W2 as indicated by limit Niza, the cusper Iwaveis displacedas shown b-y the-brokenline Hita, an i=wlf1enuL displaced'tozthe opposite limit |ll2b. ley-'broken line N3D. ,Itxwill. be observed thatthe signalwave varies the cusps |33, |34, |35 and :|36 in pushpull vmanner towardV and away from each other therebysuccessively decreasingand. increasing the time interval between successive cusps.

IFor transmission purposestthe'cusps are preferably clipped from the wave by a known clipper and shaper H8 and shaped to form a train4 of substantially narrowl width pulses .138.

The TM pulse output from modulator; :12e will be a train .of pulses similar to the pulse train |38, but due t0 the actionzof phase:shifteralzubl'the pulses from modulator'l will be. out. of. phase with the pulsesfrom 4modulator ||5 similarly as in the casev of pulse trains .35 and -32 of curves a. and b, Fig; l. Thus when these pulse=trains are combined for application to translator. .1.39, the pulses from modulator |.2Elnwill 'alternate with the pulses from modulator H0.

When a T-M transmitting .system .such as shown in Fig. 4 is employed, means must beprovided inthe vreceiver for demodulating these TM pulses. Fig. 5 illustrates. a TM demodulatoriZa which may be incorporated inthe receiving cirlcuit of Fig. 3 to replace the pulse amplitudeE demodulating or iiltercircuits 82 and Bil. The-odd TM pulses (such as the train of TM pulses '|33 of Figs. 4 and 6, for example) Ipassed by the -keyer tube 'l0 across resistor .la are applied over a connection |40 to a frequency selector rifl'which serves to shock-excites. high ffQ circuit Mil to produce a continuous wave |46, Fig. 6, which preferablyis an even harmonic oftherb-a-se wave E52 produced by thegenerator lrl of Fig. 4. The wave |45, however, is preferably of afrequency which corresponds tofthe pulse repetition rate. I Curve aofFig. 6 represents avshorttrain fof a substantially linearly increasing signal wave. Curve b shows awave "|66 in timed relation to the pulses |35 and afundamental wave |48 which is obtainedfrom wave M6- by means of a frequency divider E50 which is inductively coupled to the circuit Mil. The wave |48 is called a -fundamental wave because the period thereof corresponds tothe pulse cadence period between alternate pulses as indicated at T on curve aof Fig. 6.

'Either the initial wave |46 or the fundamental wave |48 may be used for demodulation purposes, but an odd harmonic of the fundamental wave |48 is preferred. The fundamental wave' |118, therefore.. is applied to a frequency multiplier |52 whereby a desired odd harmonicwave |54, curve c, is obtained. While wave |54 is shown for purposes of illustration to be the third harmonic of the wave |48, a higher odd harmonic .may be preferred in some cases.

. AY-phase'shifter |56 is provided in the v.output of the frequency multiplier to shift the demodulating wave in phase` with respect. to .the. TM pulses. The demodulating wave |54 is. .applied directly to amixerunit |53 for translation .of the signal intelligence 7 time displacement of the pulses into amplitude displacement.

The TM pulses |38 are applied to the unit |58 through an amplifier |60. The intelligence signals conveyed by the TM pulses are passed from the output |62 of the unit |58 through a lowpass lter |64 to the output lead 15 for reproduction in conjunction with the intelligence wave of the other branch the same as in Fig. 3.

Assuming that the sine wave |54 is used as the demodulating wave, the sine wave will be applied to the screen grid |65 of the vacuum |66. The tube is self-biased by a resistance-capacitance circuit |68. The main grid |10 is connected through coupling condenser |12 to the outlet connection |14 of the amplier |60. The plate |16 is provided with a load resistor |18 from which connection |62 is applied to the lowpass lter |64.

The self-bias of the tube N56 is such that it will not respond to the input potential of the wave |56, but will respond to the energy of the TM pulses superimposed upon the wave |54. That is to say, the tube produces a pulse output in its plate circuit whenever the combined energy of wave |54 and pulses |38 exceeds a given clipping level |86, Thus, pulses are produced at the output connection |62 which vary in amplitude according to the position of the TM pulses on the inclined portions of the wave |54. When the pulses are modulated toward each other as indicated by the arrows on the curve a of Fig. 6, the amplitude of the output pulses is increased. When the displacement modulation of the pulses is in directions away from each other the amplitude of the output pulses decreases.

This amplitude modulated pulse output, as indicated at curve d, provides a signal wave |82 in the output of the low-pass lter |64, the pulse portions defining the envelope of the signal Wave |82 being removed by the filter.

In place of the even-pulse amplitude-demodulating circuit 84 of Fig. 3 is substituted a second TM demodulating circuit which is similar in all respects to the TM demodulating circuit 82a. The output of this second demodulating circuit is fed through conductor 11 to switch 85.

While I have described above the principles of my invention in combination with specific apparatus for amplitude and time modulation of pulses, it is to be clearly understood that this description is made only by way of an example of several applications of the principles of my invention, and not as a limitation of my invention and the scope of the accompanying claims.

I claim:

1. A method of modulating a train of pulses of electrical potential comprising modulating a given characteristic of the odd pulses of said train with a given signal energy and modulating a like characteristic of the even pulses of said train with said given signal energy shifted in phase 180 from the signal energy applied to said odd pulses.

2. The method according to claim 1 wherein the modulating operations of the odd and even pulses comprise varying the amplitude of the pulses according to the respectiveV modulating signal energy.

3. The method according to claim 1 wherein the modulating operations of the odd and even pulses comprise displacing the sition according to the respective modulating signal energy.

4. A method of pulse modulation comprising pulses in time po- Y producing two series of pulses of electrical potential, the pulses of one series alternating with the pulses of the other series, modulating the pulses of said one series with signal energy, modulating the pulses of said other series with said signal energy displaced in phase substantially and combining the pulses of said two series into a single train of pulses.

5. A method of pulse modulation comprising producing two series of pulses of electrical p0- tential, the pulses of one series alternating with the pulses of the other series, modulating a given characteristic of the pulses of said one series according to a given signal energy, modulating said given characteristic of the pulses of said other series with said given signal energy shifted substantially 180 out of phase with the signal energy applied to said one series, and modulating said given characteristic of the pulses of both series with a further signal energy.

6. A method of private communication comprising generating two series of pulses of electrical potential, the pulses of one series alternating with the pulses of the other series, modulating a characteristic of the pulses of one series with a given signal energy, modulating a like characteristic of the pulses of the other series With said given signal energy shifted substantially 180 out of phase with the signal energy applied to said one series, combining the pulses of both series into a train, transmitting said train of pulses, receiving said train of pulses at a receiving point,

series of pulses, and demoduat least one of the two series to reproduce said signal energy.

7. A method according to claim 6 further including demodulating the pulses of the other of the two series, shifting in phase 180 the signal energy obtained from one of said two series, and combining the the signal energy obtained from the other of said two series. Y

8. A method of private communication comprising generating two series of pulses of electrical potential, the pulses of one series alternating in time with the pulses of the other series, modulating a given characteristic of the pulses of said one series according to a given signal energy, modulating said given characteristic of the pulses of said other series with said given signal energy shifted substantially 180 out of phase with the signal energy applied to said one series, modulating both series of pulses with a further signal energy, combining the pulses of both series into a single train, transmitting said train of pulses, receiving said train of pulses at a receiving point, separating the twoseries of pulses, demodulating to audio waves the pulses of the two series, shifting 180 in phase the audio wave derived from one of said series, combining said phase shifted audio wave with the other audio wave to cancel out said further signal, and reproducing the intelligence of said given signal energy from the combined audio wave.

communication commodulating a given characteristic of the pulses of said one series according to a given signal energy, modulating said given characteristic of the pulses of said other series with said given signal energy shifted substantially 180 out of phase with the signal energy applied to said one series, modulating both series of pulses with a further phase shifted signal energy withY signal energy, combining the pulses oi both series into a single train, transmitting said train of pulses, receiving said train of pulses at a receiving point, separating the two series of pulses, demodulating to audio waves the pulses of the two series, combining the audio waves derived from the two series to cancel out said given signal enn ergy leaving said further signal energy, and reproducing the intelligence of said further signal energy.

10. A method of reproducing the intelligence of a given signal energy from a train of pulses of electrical potential wherein the odd pulses are modulated with said energy and the even pulses are modulated with the same energy shifted 180 in phase; comprising separating the odd pulses from the even pulses, demodulating to audio waves the signal energy with which pulses of the two series are modulated, shifting 180 in phase one of the audio waves, combining the phase shifted audio wave with the other audio wave, and reproducing the intelligence of the combined audio waves.

11. A method of reproducing the intelligence of a given signal energy from a train of pulses of electrical potential wherein the odd pulses are modulated with said energy, the even pulses are modulated with the same energy shifted 180 in phase and both odd and even pulses are further modulated by an undesired signal energy; comprising separating the odd pulses from the even pulses, demodulating to audio waves the signal energy with which pulses of the two series are modulated, shifting 180 in phase one of the audio waves, combining the phase shifted audio wave with the other audio wave to cancel out said undesired signal energy, and reproducing the intelligence of said given signal energy from the combined audio waves.

12. A modulator system comprising means for producing a train of pulses of electrical potential, means to modulate a given characteristic of the odd pulses with a given signal energy, and means' to modulate said given characteristic of the even pulses with said given signal energy shifted in phase 180 from the signal energy applied to the odd pulses.

13. A system according to claim 12 wherein the two modulating means are arranged tovary the amplitude of the pulses according to the instantaneous value of the respective modulating signal energy.

14. A system according to claim 12 wherein the two modulating means are arranged t displace the time position of the pulses according to the instantaneous value of the respective modulating signal energy.

15. A pulse modulating system comprising means for producing two series of pulses of electrical potential, the pulses of one series alternating with the pulses of the other series, modulator means for the pulses of said one series, modulator means for the pulses of the other of said series, a source of signal energy, means to apply said signal energy at 180 difference in phase to the two modulator means, and means for combining th'e pulse output of the two modulator means into a single train of pulses.

16. A system according to claim 15 wherein said means for applying energy to said two modulator means includes means for applying a further 0 Number signal energy in phase to the two modulator means.

17. A private communication system comprising means for producing a train of pulses of electrical potential, means to modulate a given characteristic of the odd pulses with a given signal energy, means to modulate the even pulses withk said given signal energy shifted in phase from the signal energy applied to the odd pulses, means for transmitting the train of pulses thus modulated, means for receiving said train of pulses at a receiving point, means for separating the odd pulses from the even pulses, and means for demodulating one of the series of pulses from said separating means to reproduce said given signal energy.

18. A system for reproducing the intelligence of a given signal from a train of pulses of electrical potential wherein th'e odd and even pulses are modulated with said energy at 180 difference in phase; comprising means for separating the odd pulses from the even pulses, means for demodulating to audio waves the intelligence with which the odd and even pulses are modulated, means for shifting 180 in phase one of the audio waves, means for combining the phase shifted audio wave with the other audio wave, and means for reproducing the intelligence of the combined audio waves.

19. A system for reproducing the intelligence of a given signal energy from a train of pulses of electrical potential wherein the odd and even pulses are modulated with said energy at 180 dilerence in phase, and further modulated with an undesired signal energy in phase with respect to the odd and even pulses; comprising means for separating the odd pulses from the even pulses, means for democlulating to audio waves the intelligence with which the odd and even pulses are modulated, means for shifting 180 in phase one of th'e audio waves, means for combining the phase shifted audio wave with the other audio wave to cancel out said undesired signal energy, and means reproducing the intelligence of said given signal energy from the combined audio waves.

20. A system for reproducing the intelligence oi a given signal energy from a train of pulses of electrical potential wherein the odd and even pulses are modulated with said energy at 180 diierence in phase, and further modulated with a further signal energy in phase with respect to the odd and even pulses; comprising means for separating the odd pulses from the even pulses, means for demodulating to audio waves th'e intelligence with which the odd and even pulses are modulated, means for combining the two audio waves to cancel out said given signal energy, and means for reproducing the intelligence of said further signal energy from the combined audio waves. l

IRVING A. KRAUSE.

REFERENCES CllTED The following references are of record in the file of this patent:

FOREIGN PATENTS Country Date 

